When one refers to the MEA, the reference is to the teachers union, and primarily to the leadership, which does not necessarily reflect the views of the membership.

Not all MEA members are middle class.  Some, regrettable, are poor, and some are in the upper class (although that is most likely the effect of being married to someone who is doing well).

So, therefore and thus, saying that the Governess's constituency is not the 'middle class' but does include the MEA does NOT suggest that teachers are not middle class.